Dr. Jeff Hersh: Transient global amnesia explains sudden memory loss

Q: My aunt was really upset when she found out her dad, my grandfather, died, and she had a sudden episode where she could not remember where she was or even what day it was. Was she just in shock?

Dr. Jeff Hersh

Q: My aunt was really upset when she found out her dad, my grandfather, died, and she had a sudden episode where she could not remember where she was or even what day it was. We took her to the emergency room, and all the tests they did were normal, and she got better six hours later. Was she just in shock?

A: It sounds like your aunt may have had an episode of transient global amnesia, an uncommon condition affecting around 5 in every 100,000 Americans, though it affects as many as 25 per 100,000 of those age 50 or older.

Many TGA patients have a precipitating factor, such as physical exertion, emotional stress, pain, cold-water exposure or sexual activity. The classic symptom of TGA is the acute loss of the ability to acquire new memories, called anterograde memory loss.

There is also often the loss of, or impaired ability to access, recent past memories, called retrograde amnesia. The retrograde amnesia is typically patchy and may be for the hours, days, months or even, occasionally, years prior to the TGA episode, and it is often subtle. Memory of things that happened in the more distant past is typically preserved.

During an attack of TGA, the patient speaks and thinks normally, though the memory issues may make it seem like they are confused. They may repetitively ask the same simple questions, such as "Where am I?" or "How did I get here?" since they are not able to form a new memory of the answers they receive.

The criteria for a diagnosis of TGA are:

A reliable observer can give the history of what happened.

Anterograde memory is affected.

There is no clouding of consciousness, no impairment of functioning and no focal neurological symptoms, such as speech problems, vision problems, weakness of the face or body, change in sensation or other symptoms that would suggest a stroke.

There is nothing to suggest the patient had a seizure and no history of seizures for at least the previous two years.

There are no intoxicating substances, such as alcohol or benzodiazepines, in the patient's system.

There was no recent head trauma, since somewhat similar symptoms can occur from a concussion.

The symptoms last less than 24 hours; most commonly, they last only two to eight hours.

The cause of TGA is not known. It has been theorized that a decrease in blood flow to the areas of the brain responsible for memory may be the cause, however, there is no increased risk of stroke for people who have had TGA. In addition, it is not thought that any loss of blood flow is because of a blockage of an artery like that seen in mini-strokes, or transient ischemic attacks.

Some authors theorize that TGA may be an atypical migraine; however, even though there is an increased incidence of either a personal or family history of migraines in people having TGA, most TGA patients do not have migraines.

Patients with TGA typically have a fast and complete recovery, though 25 percent will have a recurrence in their lifetimes, with about 3 to 5 percent having a recurrence in the first year. However, less than 3 percent of TGA patients will have more than three episodes in their lifetime, so this is usually not a chronic condition.

The evaluation of TGA is focused on ruling out other conditions that can cause memory loss:

An imaging study like a CT or MRI scan may be done since, though rare, a bleed into the brain or even a brain tumor can cause memory problems if they affect the parts of the brain associated with memory acquisition.

Atypical seizures, or even the phase after a typical seizure where a patient can seem confused, called a post-ictal phase, may be evaluated.

Toxic or metabolic causes are typically ruled out by blood or urine tests.

Alcoholics can develop a syndrome where they develop memory problems; however, the symptoms from this are not usually acute in onset.

If you or a loved one develops acute memory issues, you should go to the nearest emergency room to be evaluated.

Although a TGA is scary for both the patient and the patient's family, transient global amnesia is a benign condition with an excellent prognosis.